Tokkai 2001-143736 published by the Japanese Patent Office in 2001 discloses a technique of preventing a fuel cell system from freezing even when an external temperature is below freezing point. In this technique, the temperature of the fuel cell is monitored and the fuel cell is maintained at a temperature greater than freezing point until start-up operations for the fuel cell system are commenced.
Tokkai Hei08-273689 published by the Japanese Patent Office in 1996 discloses a technique which allows pure water used in the fuel cell system to freeze. However the pure water is stored before freezing in a designated tank and is melted when start-up operations for the fuel cell system are commenced.